Chair back



FIG. 1 is a top, rear perspective view of a chair back illustrating my new design.

FIG. 2 is a bottom, front perspective view thereof.

FIG. 3 is a left side view thereof.

FIG. 4 is a front view thereof.

FIG. 5 is a right side view thereof.

FIG. 6 is a rear view thereof.

FIG. 7 is a top view thereof; and,

FIG. 8 is a bottom view thereof.

Portions of the chair back shown as evenly-sized broken lines form no part of the claimed design. Long-short broken lines are boundaries that form no part of the claimed design. 

CLAIM The ornamental design for a chair back, as shown and described. 